The present invention relates to the field of electron-beam diodes, and, more specifically, to vacuum/pressure barriers located between the vacuum environment surrounding the beam generation means and the gaseous environment into which the beam is directed in an excimer laser.
Current technology for handling the transition of an electron beam from its genesis to the adjacent gaseous environment in an excimer laser presents many limitations on the efficiency of a vacuum diode. This is primarily because of the different environments required for the vacuum diode and the adjoining laser gas cavity. While a vacuum is required for the diode, the environment of the laser cavity is typically at a pressure of 600-900 Torr.
Supported metal foils, commonly of titanium, have been widely used to provide this separation of environments, but often serve to attenuate the beam, scatter the beam's particles, or become hot due to the beam. These foils require massive support structures, known as Hibachis, which themselves intercept and greatly attenuate the beam. It is common for beam losses due to impingement by the electrons on the hibachi and attenuation by the metal foil to be as high as 60-70%.
Hibachis often cast shadows which are substantially larger than their cross sectional areas. This is because the electron beam is seldom normally incident due to the effects of the self-field generated by the beam. This can be a particularly serious problem for large amplifiers where the electron beam may have an area of several square meters.
In searching for a barrier to replace metal foils, it is important to recognize the requisite properties for use in an excimer laser system. The large difference in pressure between the vacuum of the diode and the laser cavity containing the corrosive gas challenges any barrier material. Therefore, the barrier must have high tensile strength and a high elastic modulus. It additionally must allow for high electron transmission, and have low ultraviolet reflectively. It must also be chemically compatible with fluorine or other reactive gasses.
Recent years have seen great advances in the development of ultra high strength, low-Z filaments, principally made of boron and carbon. These materials make possible the creation of an excellent replacement for the metal foil barriers of the past. The present invention uses such filaments formed into a matrix and sandwiched between layers of solid material to form a composite foil. Having strength greater than that of metal foils, the present invention allows use of support structures with ribs much more widely separated than with metal foils, and, in some cases, even allows for a completely self-supporting barrier.
Testing has revealed that barriers according to the present invention allow approximately 85% of available electrons to enter the gaseous region of an excimer laser. This compares very favorably with the approximately 35%-40% efficiency of prior hibachi supported foil barriers.
It is therefore an object of the present invention to provide a vacuum barrier which will permit greater electron through put than previous barriers.
It is another object of the present invention to provide a vacuum barrier which requires less supporting structure than previous barriers.